Cold shrink article for electrical device

ABSTRACT

A cold shrink article comprising a shaped,stretched and cured composition comprising (i) a blend of silane-grafted ethylene-α-olefin elastomer and a hydroxyl-terminated polyorganosiloxane, (ii) a vinyl-terminated silicone rubber, and (iii) an ethylene-α-olefin elastomer.

FIELD OF THE INVENTION

This invention relates to wire and cable accessories, such as splicesand terminations.

BACKGROUND OF THE INVENTION

Various technologies exist for the installation of cable accessories(e.g., splices, terminations). Cold shrink type accessories arepreferred over pre-molded push-on and heat shrink products since arelatively insignificant physical force is required for installation ascompared to the push-on type, and no heating is required versus theheat-shrink type. With the cold shrink approach, the part (e.g. a cablesplice) is factory pre-stretched unto a solid removable core, and itslides freely onto the cable. During installation, once the metalconductors are joined together for electrical continuity, the splice isproperly positioned at the center of the connection and the removablecore (e.g. a plastic spiral core) is removed allowing the rubbery spliceto shrink into place in the radial direction for a tight fit over thecable. One key requirement for this technology is the elastic recoveryof the article once installed to ensure a tight seal in order to preventmoisture ingress into the electrical connection.

Cold Shrink accessories are generally manufactured from crosslinkedsilicone rubber which exhibits excellent elastic recovery. Both hightemperature vulcanized (HTV) gums and liquid silicone rubber (LSR) areused. However, end users (e.g., electrical utilities) have reporteddeficiency in tear strength which leads to rapid tear propagation if theconnector is nicked during installation or comes into contact with asharp object during its service life. Many of the applications involveburied cable, e.g., underground installation. Another deficiency ofsilicone rubber is its relatively lower dielectric strength as comparedto an olefin elastomer for example.

SUMMARY OF THE INVENTION

This invention is a new cold shrink accessories technology that deliversthe required elastic recovery for a tight connection but with improvedtensile and tear resistance as well as dielectric strength for higherconnection reliability and potentially slimmer designs. The inventionuses reactively compatibilized olefin-silicone rubber compounds thatdelivers an improved balance of mechanical and electrical properties ofthe cold shrink article at a reduced overall cost.

In one embodiment the invention is a composition comprising a:

-   -   (A) Blend of silane-grafted ethylene-α-olefin elastomer and a        hydroxyl-terminated polyorganosiloxane;    -   (B) 70 or more, or greater than 70 to 95, or 75 to 90, or 78 to        85, weight percent (wt %), based on the weight of the        composition, of a vinyl-terminated silicone rubber;    -   (C) Crosslinking catalyst;    -   (D) Ethylene-α-olefin elastomer; and    -   (E) Optionally, one or more of an additive and filler.        In one embodiment an additive is present, and it is at least one        of a plasticizer, wax, cure promoter, adhesion promoter and        scorch inhibitor.

In one embodiment the invention is a process for making a cold shrinkarticle, the process comprising the steps of:

-   -   (1) Forming a homogeneous composition comprising:        -   (A) Blend of silane-grafted ethylene-α-olefin elastomer and            a hydroxyl-terminated polyorganosiloxane;        -   (B) 70 or more, or greater than 70 to 95, or 75 to 90, or 78            to 85, wt %, based on the weight of the composition, of a            vinyl-terminated silicone rubber;        -   (C) Crosslinking catalyst;        -   (D) Ethylene-α-olefin elastomer; and        -   (E) Optionally, one or more of an additive and filler;    -   (2) Forming the homogeneous composition into a shaped article;    -   (3) At least partially curing the shaped article;    -   (4) Degassing the at least partially cured shaped article;    -   (5) Stretching the cured, shaped article; and    -   (6) Maintaining the stretched, cured, shaped article in a        stretched state.        In one embodiment an additive is present, and it is at least one        of a plasticizer, wax, cure promoter, adhesion promoter and        scorch inhibitor. In one embodiment the cured, stretched shaped        article is maintained in the stretched state by mechanical        means, e.g., a plastic spiral core. In one embodiment the cured,        stretched shaped article is maintained in the stretched state        until the article is put into its intended use.

In one embodiment the invention is a cold shrink article made from acomposition comprising:

-   -   (A) Blend of silane-grafted ethylene-α-olefin elastomer and a        hydroxyl-terminated polyorganosiloxane;    -   (B) 70 or more, or greater than 70 to 95, or 75 to 90, or 78 to        85, wt %, based on the weight of the composition, of a        vinyl-terminated silicone rubber;    -   (C) Crosslinking catalyst;    -   (D) Ethylene-α-olefin elastomer; and    -   (E) Optionally one or more of an additive and filler.        In one embodiment the cold shrink article is a cold shrink        splice. In one embodiment an additive is present, and it is at        least one of a plasticizer, wax, cure promoter, adhesion        promoter and scorch inhibitor. In one embodiment the cold shrink        article is stretched and maintained in a stretched state by        mechanical means, e.g., a plastic spiral core.

In one embodiment the invention is a cold shrink article comprising ashaped, stretched and cured composition comprising (i) a blend ofsilane-grafted ethylene-α-olefin elastomer and a hydroxyl-terminatedpolyorganosiloxane, (ii) a vinyl-terminated silicone rubber, and (iii)an ethylene-α-olefin elastomer. In one embodiment the article furthercomprises at least one of an additive and filler. In one embodiment thecold shrink article is a cold shrink splice. In one embodiment anadditive is present, and it is at least one of a plasticizer, wax, curepromoter, adhesion promoter and scorch inhibitor. In one embodiment thecold shrink article is stretched and maintained in a stretched state bymechanical means, e.g., a plastic spiral core.

In one embodiment the invention is a cable having an external layer andcomprising a cold shrink splice, the splice shrunk about and in contactwith the external layer of the cable and comprising a shaped and curedcomposition, the composition comprising (i) a blend of silane-graftedethylene-α-olefin elastomer and a hydroxyl-terminatedpolyorganosiloxane, (ii) a vinyl-terminated silicone rubber, and (iii)an ethylene-α-olefin elastomer. In one embodiment an additive is presentin the composition of the splice, and the additive is at least one of aplasticizer, wax, cure promoter, adhesion promoter and scorch inhibitor.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Definitions

All references to the Periodic Table of the Elements refer to thePeriodic Table of the Elements published and copyrighted by CRC Press,Inc., 2003. Also, any references to a Group or Groups shall be to theGroup or Groups reflected in this Periodic Table of the Elements usingthe IUPAC system for numbering groups. Unless stated to the contrary,implicit from the context, or customary in the art, all parts andpercents are based on weight and all test methods are current as of thefiling date of this disclosure. For purposes of U.S. patent practice,the contents of any referenced patent, patent application or publicationare incorporated by reference in their entirety (or its equivalent USversion is so incorporated by reference) especially with respect to thedisclosure of synthetic techniques, product and processing designs,polymers, catalysts, definitions (to the extent not inconsistent withany definitions specifically provided in this disclosure), and generalknowledge in the art.

The numerical ranges in this disclosure are approximate, and thus mayinclude values outside of the range unless otherwise indicated.Numerical ranges include all values from and including the lower and theupper values, in increments of one unit, provided that there is aseparation of at least two units between any lower value and any highervalue. As an example, if a compositional, physical or other property,such as, for example, molecular weight, viscosity, melt index, etc., isfrom 100 to 1,000, then the intent is that all individual values, suchas 100, 101, 102, etc., and sub ranges, such as 100 to 144, 155 to 170,197 to 200, etc., are expressly enumerated. For ranges containing valueswhich are less than one or containing fractional numbers greater thanone (e.g., 1.1, 1.5, etc.), one unit is considered to be 0.0001, 0.001,0.01 or 0.1, as appropriate. For ranges containing single digit numbersless than ten (e.g., 1 to 5), one unit is typically considered to be0.1. These are only examples of what is specifically intended, and allpossible combinations of numerical values between the lowest value andthe highest value enumerated, are to be considered to be expresslystated in this disclosure. Numerical ranges are provided within thisdisclosure for, among other things, the amounts ofSi-g-ethylene-α-olefin elastomer, silicone rubber, crosslinkingcatalyst, ethylene-α-olefin elastomer, additives and filler in thecomposition, and the various characteristics and properties by whichthese components are defined.

As used with respect to a chemical compound, unless specificallyindicated otherwise, the singular includes all isomeric forms and viceversa (for example, “hexane”, includes all isomers of hexaneindividually or collectively). The terms “compound” and “complex” areused interchangeably to refer to organic-, inorganic- and organometalcompounds.

The term “or”, unless stated otherwise, refers to the listed membersindividually as well as in any combination.

“Composition” and like terms mean a mixture or blend of two or morecomponents.

“Blend,” “polymer blend” and like terms mean a blend of two or morepolymers. Such a blend may or may not be miscible. Such a blend may ormay not be phase separated. Such a blend may or may not contain one ormore domain configurations, as determined from transmission electronspectroscopy, light scattering, x-ray scattering, and any other methodknown in the art.

“Polymer” means a polymeric compound prepared by polymerizing monomers,whether of the same or a different type. The generic term polymer thusembraces the term homopolymer, usually employed to refer to polymersprepared from only one type of monomer, and the term interpolymer asdefined below. It also embraces all forms of interpolymers, e.g.,random, block, homogeneous, heterogeneous, etc. The terms“ethylene/α-olefin polymer” and “propylene/.alpha.-olefin polymer” areindicative of interpolymers as described below.

“Interpolymer” means a polymer prepared by the polymerization of atleast two different monomers. This generic term includes copolymers,usually employed to refer to polymers prepared from two differentmonomers, and polymers prepared from more than two different monomers,e.g., terpolymers, tetrapolymers, etc.

“Elastomer” and like terms means a rubber-like polymer that can bestretched to at least twice its original length and which retracts veryrapidly to approximately its original length when the force exerting thestretching is released. An elastomer has an elastic modulus of about10,000 psi (68.95 MPa) or less and an elongation usually greater than200% in the uncrosslinked state at room temperature using the method ofASTM D638-72.

“Ethylene-α-olefin elastomer” and like terms mean an elastomeric polymercomprising at least 50 mol % units derived from ethylene and betweengreater than zero and 50 mol % of units derived from an α-olefin, e.g.,propylene, butene, hexene, octene, etc. “Derived from” means, in thecontext of this definition, that the units in the polymer backboneand/or polymer branches are a result of the polymerization orcopolymerization of the monomers from which the polymer is made.

“Crosslinked”, “cured” and similar terms mean that the polymer, beforeor after it is shaped into an article, was subjected or exposed to atreatment which induced crosslinking and has xylene or decaleneextractables between 10 and 100 weight percent (i.e., a gel content of0-90%).

“Cable” and like terms mean at least one wire or optical fiber within aprotective insulation, jacket or sheath. Typically, a cable is two ormore wires or optical fibers bound together, typically in a commonprotective insulation, jacket or sheath. The individual wires or fibersinside the jacket may be bare, covered or insulated. Combination cablesmay contain both electrical wires and optical fibers. The cable, etc.can be designed for low, medium and high voltage applications. Typicalcable designs are illustrated in U.S. Pat. Nos. 5,246,783, 6,496,629 and6,714,707.

“Cold shrink” and like terms refer to an open ended sleeve, madeprimarily from elastomers with high-performance physical properties,that has been factory expanded, or pre-stretched, and assembled onto asupporting removable plastic core. Cold shrink tubing shrinks uponremoval of that supporting core during the installation process. In oneembodiment, an electrician slides the tube over a cable to be spliced orterminated and unwinds the core, causing the tube to collapse down, orcontract, in place.

Silane-Grafted Ethylene-α-Olefin Elastomer (Si-g-Ethylene-α-OlefinElastomer) Ethylene-α-Olefin Elastomers

The Si-g-ethylene-α-olefin elastomer that is blended withhydroxyl-terminated polyorganosiloxane to form the first (i.e., A)component of the composition of this invention is an interpolymer ofethylene and an α-olefin and that has been grafted with a silane.Examples of the pre-grafted ethylene-α-olefin interpolymers are theethylene/α-olefin interpolymers in which the α-olefin is typically aC₃₋₂₀, more typically a C₃₋₁₂ and even more typically a C₃₋₈, linear,branched or cyclic α-olefin. Examples of C₃₋₂₀ α-olefins includepropene, 1-butene, 4-methyl-1-pentene, 1-hexene, 1-octene, 1-decene,1-dodecene, 1-tetradecene, 1-hexadecene, and 1-octadecene. The α-olefinscan also contain a cyclic structure such as cyclohexane or cyclopentane,resulting in an α-olefin such as 3-cyclohexyl-1-propene (allylcyclohexane) and vinyl cyclohexane. Although not α-olefins in theclassical sense of the term, for purposes of this invention certaincyclic olefins, such as norbornene and related olefins, are α-olefinsand can be used in place of some or all of the α-olefins describedabove. Similarly, styrene and its related olefins (for example,α-methylstyrene, etc.) are α-olefins for purposes of this invention.Illustrative polyethylene copolymers include ethylene/propylene,ethylene/butene, ethylene/1-hexene, ethylene/1-octene, ethylene/styrene,and the like. Illustrative terpolymers includeethylene/propylene/l-octene, ethylene/propylene/butene,ethylene/butene/1-octene, and ethylene/butene/styrene. The copolymerscan be random or blocky.

More specific examples of pre-grafted ethylene-α-olefin elastomersuseful in this invention include very low density polyethylene (VLDPE)(e.g., FLEXOMER™ ethylene/1-hexene polyethylene made by The Dow ChemicalCompany), homogeneously branched, linear ethylene/α-olefin copolymers(e.g. TAFMER™ by Mitsui Petrochemicals Company Limited and EXACT™ byExxon Chemical Company), homogeneously branched, substantially linearethylene/α-olefin polymers (e.g., AFFINITY™ and ENGAGE™ polyethyleneavailable from The Dow Chemical Company), and olefin block copolymerssuch as those described in U.S. Pat. No. 7,355,089 (e.g., INFUSE™available from The Dow Chemical Company). The more preferred pre-graftedethylene-α-olefin elastomers are the homogeneously branched linear andsubstantially linear ethylene-α-olefin elastomers. The substantiallylinear ethylene-α-olefin elastomers are especially preferred, and aremore fully described in U.S. Pat. Nos. 5,272,236, 5,278,272 and5,986,028.

Blends of any of the above ethylene-α-olefin elastomers can also be usedas the component that is grafted with a silane and then blended with thepolyorganosiloxane to form the first component of the composition ofthis invention, and the ethylene-α-olefin elastomers can be blended ordiluted with one or more other polymers to the extent that, in apreferred mode, the ethylene-α-olefin elastomers that are silane-graftedand then used to form the blend with the polyorganosiloxane constituteat least about 50, preferably at least about 75 and more preferably atleast about 80, weight percent (wt %) of the silane-graftedethylene-α-olefin elastomer component that is blended with thepolyorganosiloxane.

The ethylene-α-olefin elastomers useful in the practice of thisinvention typically have, before grafting, a density of less than 0.925,more typically less than 0.915, and even more typically less than 0.905,grams per cubic centimeter (g/cm³). The ethylene-α-olefin elastomerstypically have a density greater than 0.85, more typically greater than0.86 and even more typically greater than 0.865, g/cm³. Density ismeasured by the procedure of ASTM D-792. Generally, the greater theα-olefin content of the elastomer, the lower the density and the moreamorphous the elastomer. Low density polyolefin interpolymers aregenerally characterized as semi-crystalline, flexible and having goodoptical properties, e.g., high transmission of visible and UV-light andlow haze.

Silane and Silane Grafting

The ethylene-α-olefin elastomer is grafted with a silane before blendingwith the polyorganosiloxane to form the Si-g-ethylene-α-olefinelastomer/polyorganosiloxane blend component of the composition of thisinvention. A Si-g-ethylene elastomer as used herein is an ethyleneelastomer as described above that is grafted with at least one silanecompound.

In an embodiment, the Si-g-ethylene-α-olefin elastomer has a molecularweight distribution from about 1 to 7, or from 1.5 to 6, or from 2 to 5.

In an embodiment, the Si-g-ethylene-α-olefin elastomer has a densityfrom 0.855 g/cc to 0.955 g/cc, or from 0.86 g/cc to 0.90 g/cc, or from0.865 g/cc to 0.895 g/cc.

In an embodiment, the amount of silane used in the grafting reaction isgreater than, or equal to, 0.05 parts per hundred (“phr” based on theamount of the ethylene-α-olefin elastomer), or from 0.5 phr to 6 phr, orfrom 0.5 phr to 4 phr.

In an embodiment the amount of amount of initiator used in the graftingreaction is less than, or equal to, 4 millimoles radicals per 100 gramsethylene-α-olefin elastomer, or less than, or equal to, 2 millimolesradicals per 100 grams ethylene-α-olefin elastomer, or less than, orequal to, 1 millimoles radicals per 100 grams ethylene-α-olefinelastomer.

In an embodiment the amount of silane constituent grafted on theethylene-α-olefin elastomer chain is greater than, or equal to, 0.05 wt% (based on the weight of the ethylene-α-olefin elastomer), asdetermined by FTIR analysis, or other appropriate method. In a furtherembodiment this amount is greater than, or equal to, 0.5 wt %, and inyet a further embodiment this amount is greater than, or equal to, 1.2wt %. In an embodiment the amount silane constituent grafted on theethylene-α-olefin elastomer is from 0.5 wt % to 5.0 wt %.

Suitable silanes include, but are not limited to, those of the generalformula (I):CH₂═CR—(COO)_(x)(C_(n)H_(2n))_(y)SiR₃  (I).

In this formula, R is a hydrogen atom or methyl group; x and y are 0 or1, with the proviso that when x is 1, y is 1; n is an integer from 1 to12 inclusive, or 1 to 4, and each R′ independently is an organic group,including, but not limited to, an alkoxy group having from 1 to 12carbon atoms (e.g. methoxy, ethoxy, butoxy), an aryloxy group (e.g.phenoxy), an araloxy group (e.g. benzyloxy), an aliphatic or aromaticsiloxy group, an aromatic acyloxyl group, an aliphatic acyloxy grouphaving from 1 to 12 carbon atoms (e.g. formyloxy, acetyloxy,propanoyloxy), amino or substituted amino groups (alkylamino,arylamino), or a lower alkyl group having 1 to 6 carbon atoms.

In an embodiment the silane compound is selected fromvinyltrialkoxysilanes, vinyltriacyloxysilanes or vinyltrichlorosilane.In addition any silane, or mixtures of silanes, which will effectivelygraft to, and/or crosslink, the ethylene-α-olefin elastomer can be usedin the practice of this invention. Suitable silanes include unsaturatedsilanes that comprise both an ethylenically unsaturated hydrocarbylgroup, such as a vinyl, allyl, isopropenyl, butenyl, cyclohexenyl or-(meth)acryloxy allyl group, and a hydrolyzable group, such as, ahydrocarbyloxy, hydrocarbonyloxy, or hydrocarbylamino group, or ahalide. Examples of hydrolyzable groups include methoxy, ethoxy,formyloxy, acetoxy, proprionyloxy, chloro, and alkyl or arylaminogroups. Preferred silanes are the unsaturated alkoxy silanes which canbe grafted onto the elastomer. These silanes and their method ofpreparation are more fully described in U.S. Pat. No. 5,266,627 toMeverden, et al.

In an embodiment silanes include vinyltrimethoxysilane (VTMS),vinyltriethoxysilane, 3-(trimethoxysilyl)propyl methacrylate(-(meth)acryloxypropyl trimethoxysilane), and mixtures thereof.

The silane can be grafted to the ethylene-α-olefin elastomer by anyconventional method, typically in the presence of a free radicalinitiator, for example peroxides and azo compounds, etc., or by ionizingradiation. Organic initiators are preferred, such as any one of theperoxide initiators, for example, dicumyl peroxide, di-tert-butylperoxide, t-butyl perbenzoate, benzoyl peroxide, cumene hydroperoxide,t-butyl peroctoate, methyl ethyl ketone peroxide,2,5-dimethyl-2,5-di(tert-butyl peroxy)hexane, lauryl peroxide, andtert-butyl peracetate. A suitable azo compound is2,2′-azobis(isobutyronitrile).

The amount of initiator and silane employed will affect the finalstructure of the silane grafted ethylene-α-olefin elastomer, such as,for example, the degree of grafting in the grafted elastomer and thedegree of crosslinking in the cured elastomer. The resulting structure,will in turn, affect the physical and mechanical properties of the finalproduct. Typically, the amount of initiator and silane employed will notexceed that which is determined to provide the desired level ofcrosslinking, and the resulting properties in the elastomer.

The grafting reaction should be performed under conditions that maximizegrafts onto the elastomer (polymer) backbone, and minimize sidereactions, such as the homopolymerization of grafting agent, which isnot grafted to the polymer. Some silane agents undergo minimal or nohomopolymerization, due to steric features in the molecular structure,low reactivity and/or other reasons.

Hydroxyl-terminated Polyorganosiloxane (OH-terminatedPolyorganosiloxane)

The OH-terminated polyorganosiloxane component of theSi-g-ethylene-α-olefin/OH-terminated polyorganosiloxane blend that isthe first or A component of the composition of this invention typicallyhas an average unit formula R_(a)SiO_((4−a)/2) which may have a linearor partially-branched structure but is preferably linear. Each R may bethe same or different. R is a substituted or non-substituted monovalenthydrocarbon group which may be, for example, an alkyl group, such as amethyl, ethyl, propyl, butyl, and octyl groups; aryl groups such asphenyl and tolyl groups; aralkyl groups; alkenyl groups, for example,vinyl, allyl, butenyl, hexenyl, and heptenyl groups; and halogenatedalkyl groups, for example chloropropyl and 3,3,3-trifluoropropyl groups.The polyorganosiloxane is terminated with one or more hydroxyl groups.When R is an alkenyl group, the alkenyl group is preferably a vinylgroup or hexenyl group, and most preferably a vinyl group. Indeedalkenyl groups may be present in the polyorganosiloxane on terminalgroups and/or polymer side chains.

Representative OH-terminated polyorganosiloxane include, but are notlimited to, hydroxyl-terminated polydimethylsiloxane,hydroxyl-terminated polydimethylsiloxane, hydroxyl-terminated copolymerof methylvinylsiloxane and dimethylsiloxane, hydroxyl-terminatedcopolymer of methylvinylsiloxane and dimethylsiloxane,hydroxyl-terminated polydimethylsiloxane, hydroxyl-terminated copolymerof methylvinylsiloxane and dimethylsiloxane, hydroxyl-terminatedcopolymer of methylvinylsiloxane and dimethylsiloxane,hydroxyl-terminated polydimethylsiloxane, hydroxyl-terminated copolymerof methylhexenylsiloxane and dimethylsiloxane, hydroxyl-terminatedcopolymer of methylhexenylsiloxane and dimethylsiloxane,hydroxyl-terminated copolymer of methylphenylsiloxane anddimethylsiloxane, hydroxyl-terminated copolymer of methylphenylsiloxaneand dimethylsiloxane, hydroxyl-terminated copolymer ofmethyl(3,3,3-trifluoropropyl)siloxane and dimethylsiloxane, andhydroxyl-terminated copolymer of methyl(3,3,3-trifluoropropyl)siloxaneand dimethylsiloxane.

Blend of Si-g-Ethylene-α-Olefin Elastomer and OH-TerminatedPolyorganosiloxane

The blend of Si-g-ethylene-α-olefin elastomer and OH-terminatedpolyorganosiloxane typically comprises from 90 to 99.5, more typicallyfrom 93 to 99 and even more typically from 97 to 95, wt %Si-g-ethylene-α-olefin elastomer. The blend of Si-g-ethylene-α-olefinelastomer and OH-terminated polyorganosiloxane typically comprises from0.5 to 10, more typically from 1 to 7 and even more typically from 3 to5, wt % OH-terminated polyorganosiloxane. Although the blend can containone or more other components as described above, typically andpreferably the only two components of the blend are theSi-g-ethylene-α-olefin elastomer and OH-terminated polyorganosiloxane.

Vinyl-Terminated Silicone Rubber

The vinyl-terminated silicone rubber component of the compositions ofthis invention are polyorganosiloxanes as described above exceptcomprising at least one terminal vinyl group rather than at least oneterminal hydroxyl group. Representative vinyl-terminated siliconerubbers include, but are not limited to, vinyl-terminatedpolydimethylsiloxane, vinyl-terminated polydimethylsiloxane,vinyl-terminated copolymer of methylvinylsiloxane and dimethylsiloxane,vinyl-terminated copolymer of methylvinylsiloxane and dimethylsiloxane,vinyl-terminated polydimethylsiloxane, vinyl-terminated copolymer ofmethylvinylsiloxane and dimethylsiloxane, vinyl-terminated copolymer ofmethylvinylsiloxane and dimethylsiloxane, vinyl-terminatedpolydimethylsiloxane, vinyl-terminated copolymer ofmethylhexenylsiloxane and dimethylsiloxane, vinyl-terminated copolymerof methylhexenylsiloxane and dimethylsiloxane, vinyl-terminatedcopolymer of methylphenylsiloxane and dimethylsiloxane, vinyl-terminatedcopolymer of methylphenylsiloxane and dimethylsiloxane, vinyl-terminatedcopolymer of methyl(3,3,3-trifluoropropyl)siloxane and dimethylsiloxane,and vinyl-terminated copolymer of methyl(3,3,3-trifluoropropyl)siloxaneand dimethylsiloxane. Typically, if a vinyl-terminated silicone rubbercomprises both a vinyl termination and a hydroxyl termination, if isconsidered part of the rubber component of this invention.

Crosslinking Catalyst

Cure (crosslinking) of a silanated graft is promoted with a crosslinkingcatalyst (sometimes referred to as a crosslinking agent), and anycatalyst that will effectively promote the crosslinking of theSi-g-ethylene-α-olefin elastomer can be used. These catalysts generallyinclude acids and bases, and organometallic compounds, including organictitanates, organic zirconates, and complexes or carboxylates of lead,cobalt, iron, nickel, zinc and tin.

Dibutyltin dilaurate, dioctyltin maleate, dibutyltin diacetate,dibutyltin dioctoate, stannous acetate, stannous octoate, leadnaphthenate, zinc caprylate, cobalt naphthenate, and the like, can beused. The amount of catalyst will depend on the particular system atissue.

In certain embodiments, dual crosslinking systems, which use acombination of radiation, heat, moisture and/or crosslinking steps, maybe effectively employed. For instance, it may be desirable to employperoxide crosslinking agents in conjunction with silane crosslinkingagents, peroxide crosslinking agents in conjunction with radiation, orsulfur-containing crosslinking agents in conjunction with silanecrosslinking agents. Dual crosslinking systems are disclosed in U.S.Pat. Nos. 5,911,940 and 6,124,370.

Ethylene-α-Olefin Elastomer

In one embodiment the ethylene-α-olefin elastomer component of thecomposition of this invention is the same as the pre-graftedethylene-α-olefin elastomer described above.

In one embodiment the ethylene-α-olefin elastomer component of thecomposition of this invention is an ethylene-propylene-diene monomer(EPDM). The EPDM includes units derived from ethylene. The EPDM alsoincludes units derived from propylene. Olefin other than and/or inaddition to propylene may be utilized in the EPDM. Nonlimiting examplesof suitable other olefins for mixture with ethylene include one or moreC₄₋₃₀ or C₄₋₂₀ or C₄₋₁₂ aliphatic-, cycloaliphatic- oraromatic-compounds (comonomers) containing one or more ethylenicunsaturations. Examples include aliphatic-, cycloaliphatic- and aromaticolefins such as isobutylene, 1-butene, 1-pentene, 1-hexene, 1-heptene,1-octene, 1-nonene, 1-decene, and 1-dodecene, 1-tetradecene,1-hexadecene, 1-octadecene, 1-eicosene, 3-methyl-1-butene,3-methyl-1-pentene, 4-methyl-1-pentene, 4,6-dimethyl-1-heptene,vinylcyclohexane, styrene, cyclopentene, cyclohexene, cyclooctene, andmixtures.

The EPDM includes units derived from a diene. The diene can beconjugated-, non-conjugated-, straight chain-, branched chain- orcyclic-hydrocarbon diene having from 6 to 15 carbon atoms. Nonlimitingexamples of suitable diene include 1,4-hexadiene; 1,6-octadiene;1,7-octadiene; 1,9-decadiene; branched chain acyclic diene, such as5-methyl-1,4-hexadiene; 3,7-dimethyl-1,6-octadiene;3,7-dimethyl-1,7-octadiene and mixed isomers of dihydromyricene anddihydroocinene, single ring alicyclic dienes, such as1,3-cyclopentadiene; 1,4-cyclohexadiene; 1,5-cyclooctadiene and1,5-cyclododecadiene, and multi-ring alicyclic fused and bridged ringdienes, such as tetrahydroindene, methyl tetrahydroindene,dicyclopentadiene, bicyclo-(2,2,1)-hepta-2,5-diene; alkenyl, alkylidene,cycloalkenyl and cycloalkylidene norbornenes, such as5-methylene-2-norbornene (MNB); 5-propenyl-2-norbornene,5-isopropylidene-2-norbornene, 5-(4-cyclopentenyl)-2-norbornene,5-cyclohexylidene-2-norbornene, 5-vinyl-2-norbornene, norbornadiene,1,4-hexadiene (HD), 5-ethylidene-2-norbornene (ENB),5-vinylidene-2-norbornene (VNB), 5-methylene-2-norbornene (MNB), anddicyclopentadiene (DCPD). In one embodiment the diene is selected fromVNB and ENB. In one embodiment the diene is butadiene.

In one embodiment the ethylene-α-olefin elastomer component of thecomposition of this invention comprises both an EPDM and anethylene-α-olefin elastomer as previously described.

Additives and Fillers

The compositions and articles of this invention may also containadditives. Representative additives include but are not limited toantioxidants, cross linking co-agents, cure boosters and scorchretardants, processing aids, coupling agents, ultraviolet stabilizers(including UV absorbers), antistatic agents, nucleating agents, slipagents, plasticizers (particularly plasticizer oil), lubricants,viscosity control agents, tackifiers, anti-blocking agents, surfactants,extender oils, acid scavengers, flame retardants and metal deactivators.These additives are typically used in a conventional manner and inconventional amounts, e.g., from 0.01 wt % or less to 20 wt % or morebased on the weight of the composition.

Scorch inhibitors include 2,2,6,6-tetramethylpiperidinoxyl (TEMPO) and4-hydroxy-2,2,6,6-tetramethylpiperidinoxyl (4-hydroxy TEMPO). SuitableUV light stabilizers include hindered amine light stabilizers (HALS) andUV light absorber (UVA) additives. Representative UVA additives includebenzotriazole types such as TINUVIN 326 and TINUVIN 328 commerciallyavailable from Ciba, Inc. Blends of HALS and UVA additives are alsoeffective. Examples of antioxidants include hindered phenols such astetrakis [methylene(3,5-di-tert-butyl-4-hydroxyhydro-cinnamate)]methane;bis[(beta-(3,5-ditert-butyl-4-hydroxybenzyl)methyl-carboxy-ethyl)]-sulphide,4,4′-thiobis(2-methyl-6-tert-butylphenol),4,4′-thiobis(2-tert-butyl-5-methylphenol),2,2′-thiobis(4-methyl-6-tert-butylphenol), and thiodiethylenebis(3,5-di-tert-butyl-4-hydroxy)-hydrocinnamate; phosphites andphosphonites such as tris(2,4-di-tert-butylphenyl)phosphite anddi-tert-butylphenyl-phosphonite; thio compounds such asdilaurylthiodipropionate, dimyristylthiodipropionate, anddistearylthiodipropionate; various siloxanes; polymerized2,2,4-trimethyl-1,2-dihydroquinoline,n,n′-bis(1,4-dimethylpentyl-p-phenylenediamine), alkylateddiphenylamines, 4,4′-bis-(alpha,alpha-dimethylbenzyl)-diphenylamine,diphenyl-p-phenylenediamine, mixed di-aryl-p-phenylenediamines, andother hindered amine anti-degradants or stabilizers. Examples ofprocessing aids include but are not limited to metal salts of carboxylicacids such as zinc stearate or calcium stearate; fatty acids such asstearic acid, oleic acid, or erucic acid; fatty amides such asstearamide, oleamide, erucamide, or N,N′-ethylene bis-stearamide;polyethylene wax; oxidized polyethylene wax; polymers of ethylene oxide;copolymers of ethylene oxide and propylene oxide; vegetable waxes;petroleum waxes; and nonionic surfactants.

The compositions and articles of this invention may also contain filler,either conductive or nonconductive. Representative fillers include butare not limited to the various metal oxides and hydroxides, e.g.,titanium dioxide, zinc oxide, magnesium hydroxide, potassium hydroxideand aluminum trihydroxide; metal carbonates such as magnesium carbonateand calcium carbonate; metal sulfides and sulfates such as molybdenumdisulfide and barium sulfate; metal borates such as barium borate,meta-barium borate, zinc borate and meta-zinc borate; metal anhydridesuch as aluminum anhydride; silicates, carbon black, talc, clay such asdiatomite, kaolin and montmorillonite; huntite; celite; asbestos; groundminerals; and lithopone. These fillers are typically used in aconventional manner and in conventional amounts, e.g., from 5 wt % orless to 50 wt % or more based on the weight of the composition.

Cold Shrink Compositions

In one embodiment the cold shrink composition comprises based on theweight of the composition:

-   -   (A) 0.5 to 30, or 1 to 20, or 3 to 10 wt % of a blend of        silane-grafted ethylene-α-olefin elastomer and a        hydroxyl-terminated polyorganosiloxane;    -   (B) 70 or more, or greater than 70 to 95, or 75 to 90, or 78 to        85, wt % vinyl-terminated silicone rubber;    -   (C) 0.001 to 5, or 0.005 to 2, or 0.1 to 1, wt % crosslinking        catalyst;    -   (D) 0.5 to 50, or 1 to 40, or 5 to 35, wt % ethylene-α-olefin        elastomer; and    -   (E) Optionally one or more of an additive and filler.

In one embodiment the cold shrink composition further comprises, basedon the weight of the composition, from greater than zero to 40, or 1 to38 or 5 to 35, wt % of a filler.

In one embodiment the cold shrink composition further comprises, basedon the weight of the composition, from greater than zero to 20, or 0.001to 10 or 0.5 to 5, wt % of at least one additive.

In one embodiment the cold shrink composition comprises an additiveselected from the group consisting of antioxidants, cross linkingco-agents, cure boosters and scorch retardants, processing aids,coupling agents, ultraviolet stabilizers, antistatic agents, nucleatingagents, slip agents, plasticizers, lubricants, viscosity control agents,tackifiers, anti-blocking agents, surfactants, extender oils, acidscavengers, flame retardants, metal deactivators and mixtures thereof.

Compounding

Compounding of the compositions can be effected by standard equipmentknown to those skilled in the art. Examples of compounding equipment areinternal batch mixers, such as a BANBURY™ or BOLLING™ internal mixer.Alternatively, continuous single, or twin screw, mixers can be used,such as FARREL™ continuous mixer or a HAAKE™ mixer, a WERNER andPFLEIDERER™ twin screw mixer, or a BUSS™ kneading continuous extruder.The type of mixer utilized, and the operating conditions of the mixer,will affect properties of the composition such as viscosity, volumeresistivity, and extruded surface smoothness.

In one embodiment (A) the blend of silane-grafted ethylene-α-olefinelastomer and a hydroxyl-terminated polyorganosiloxane, (B)vinyl-terminated silicone rubber, (C) crosslinking catalyst, (D)vinyl-terminated silicone rubber, and (E) filler and/or additives, ifany, are mixed, typically in the described sequence, in appropriatecompounding equipment to obtain a homogeneous mixture taking care not toinduce premature crosslinking. The homogeneous mixture is then formedinto the desired shape by extrusion or molding, and then cured (or atleast partially cured). If a molded article, typically it is at leastpartially cured in the mold. The article is then typically degassed,removed from the mold (if molded), stretched to the desired size, andheld in the stretched state by mechanical means, e.g., plastic spiralcore, until ready for use. In one embodiment the article continues tocure after the completion of the extrusion or molding operation.

Articles

In one embodiment the invention is a cable accessory. In one embodimentthe invention is a cold shrink splice or termination in the form of asleeve or tube. In one embodiment the invention is a cold shrink splice.In one embodiment the invention is a cold shrink splice made from acomposition comprising:

-   -   (A) 0.5 to 30, or 1 to 20, or 3 to 10 wt % of a blend of        silane-grafted ethylene-α-olefin elastomer and a        hydroxyl-terminated polyorganosiloxane;    -   (B) 70 or more, or greater than 70 to 95, or 75 to 90, or 78 to        85, wt % vinyl-terminated silicone rubber;    -   (C) 0.001 to 5, or 0.005 to 2, or 0.1 to 1, wt % crosslinking        catalyst;    -   (D) 0.5 to 50, or 1 to 40, or 5 to 35, wt % ethylene-α-olefin        elastomer; and    -   (E) Optionally one or more of an additive and filler.

In one embodiment the invention is a cold shrink article comprising ashaped, stretched and cured composition comprising (i) a blend ofsilane-grafted ethylene-α-olefin elastomer and a hydroxyl-terminatedpolyorganosiloxane, (ii) a vinyl-terminated silicone rubber, and (iii)an ethylene-α-olefin elastomer.

In one embodiment the invention is a cable having an external layer andcomprising a cold shrink splice, the splice shrunk about and in contactwith the external layer of the cable and comprising a shaped and curedcomposition, the composition comprising (i) a blend of silane-graftedethylene-α-olefin elastomer and a hydroxyl-terminatedpolyorganosiloxane, (ii) a vinyl-terminated silicone rubber, and (iii)an ethylene-α-olefin elastomer.

EXAMPLES

Test Methods

Tear Die B is reported in kiloNewtons per meter (kN/m), and it ismeasured by ASTM D624 Type B. Tear tests are conducted on an INSTRON™5565 tester at a speed of 500 millimeters per minute (mm/min).

Tensile Strength is reported in MegaPascals (MPa), and it is measured inaccordance with ASTM D638 Type 4. Tensile tests are conducted on anINSTRON™ 5565 tensile tester at a speed of 500 mm/min.

Tensile Elongation is reported as a percent over the original length ofthe sample, and it is measured in accordance with ASTM D638 Type 4.Tensile tests are conducted on an INSTRON™ 5565 tensile tester at aspeed of 500 mm/min.

M100 is chosen as a measure of flexibility, and it is calculated as themodulus at 100% strain. M100 is reported in MegaPascals (MPa).

Tensile Set, or Tensile Permanent Set, is measured by a procedure inwhich reported one to three unstretched and conditioned specimens areplaced in the clamps of the tension set apparatus. The specimen(s) areplaced in the grips of the testing machine, using care to adjust thespecimen symmetrically to distribute tension uniformly over the crosssection. The Tension Set apparatus is set to 100% elongation andverified using a caliper. The specimens are placed in an oven at atemperature of 100° C. for 22 hours and removed to room temperature (23°C.) for 10 minutes. The samples are then removed from the Tension Setapparatus. After 10 minutes, the distance between the marked gauges ismeasured. Tensile set is calculated according to the following equationS=100(D−G)/Gwherein S is the tension set in percent, D is the distance between thegauge marks (post set), and G is the original distance between gaugemarks, or 1.0 inch (25.4 mm).

AC Breakdown Strength is reported in kilovolts per millimeter (kV/mm).The alternating current breakdown strength (ACBD) is measured onHIPOTRONICS (model 775-5-D149-P-B) at room temperature with a voltageincreasing speed of 1 kilovolt per second (kV/s).

Dissipation Factor (DF) at 90° C. are measured at 90° C. on a Q30 seriesinstrument with a frequency of 50 hertz (Hz) and the voltage of 1 kV.Before the test, sample sheets are pre-treated in a 60° C. in an ovenfor 5 days under 0.07-0.09 MPa vacuum.

Materials

SILASATIC™ GP-30 is a vinyl-terminated, peroxide-curable, siliconerubber gum available from Dow Corning.

VTMS-g-ENGAGE/OH-PDMS is a silane grafted blend (45.5 wt. % ENGAGE™ 8200and 45.5 wt. % ENGAGE™ 7467) made on a ZSK-30 twin-screw extruder, usinga total silane content of 2 wt %, resulting in an actual grafting levelof 1.5 wt. %; and the PDMS-OH content is 5 wt %. ENGAGE™ 8200 (5 MI,0.870 density) is an ethylene-octene copolymer, and ENGAGE™ 7467 (1 MI,0.860 density) is an ethylene-butene copolymer, both resins from the DowChemical Company.

DBTDL is dibutyltin dilaurate.

NORDEL IP 4520 is an amorphous ethylene-propylene-diene terpolymer(EPDM) available from The Dow Chemical Company.

PEROXIDE L-101 is 2,5-dimethyl-2,5-di(butyl peroxy)hexane.

Compositions, Procedure and Results

The compositions are compounded in HAAKE™ mixer set a temperature of 80°C. Mixing time is 10 minutes with a rotor speed of 60 revolutions perminute (rpm). Plaques are made by compression molding and cured in thepress at 170° C. for 10 minutes. The compositions and test results arereported in the Table.

TABLE Compositions and Test Results Compar- Compar- Inven- Inven- Inven-ative Ex- ative Ex- tive Ex- tive Ex- tive Ex- ample 1 ample 2 ample 1ample 2 ample 3 Silicone Rubber 100 70 80 70 70 (SILASATIC GP-30)VTMS-g-ENGAGE/ 20 5 4.95 OH-PDMS Blend DBTDL Catalyst 0.05 MB EPDMNordel 30 25 25 IP 4520 Peroxide L-101 1 1 0.8 1 1 Total (phr) 101 101100.8 101 101 Tear Die B, kN/m 31.3 22.1 46.7 34.9 35.3 TensileStrength, 4.5 4.44 6 5.8 6.3 MPa Tensile 504 447 548 425 481 Elongation,% M100 (MPa) 0.63 0.76 0.92 0.85 0.81 Tensile Set, % <5 <5 29.8 6.6 6.8AC Breakdown 22.6 19.6 26.4 28.8 30.7 Strength, kV/mm DF at 90 C., % 3.72.45 2.53 3.87 2.81

CE 1 shows the typical properties of a peroxide crosslinked siliconerubber with generally excellent tensile recovery as shown by the lowtension set, but exhibiting low tensile, tear and dielectric breakdownstrength. CE 2 shows the impact of blending an olefin elastomer (EPDM)with the silicone rubber then crosslinking with peroxide. Given theincompatibility of the two materials, the data shows no synergy in theapproach, resulting in inferior mechanical properties of the blend.Moreover, the dielectric strength is not improved.

IE 1-IE 3 represent the invention showing reactive blend approaches forimproved properties and ability to balance excellent tensile strength,higher tear resistance and higher dielectric strength along with goodelastic recovery, suitable for a cold shrink electrical application.Note, due to the tension set requirement for the application, thecomposition space for the invention uses a relatively high amount of thesilicone phase (Si-rubber content of the composition is 70% or more),essentially modifying the silicone rubber to improve the desiredproperties; unlike WO2006007268A where the Si-rubber content of thecomposition is in the range of 5-70%.

The invention claimed is:
 1. A composition comprising: (A) A blend ofsilane-grafted ethylene-α-olefin elastomer and a hydroxyl-terminatedpolyorganosiloxane; (B) 70 or more weight percent (wt %), based on theweight of the composition, of a vinyl-terminated silicone rubber; (C) Acrosslinking catalyst; (D) An ethylene-α-olefin elastomer; and (E)Optionally, one or more of an additive and filler.
 2. The composition ofclaim 1 in which the silane-grafted ethylene-α-olefin elastomer is asilane-grafted ethylene-propylene elastomer.
 3. The composition of claim2 in which the hydroxyl-terminated polyorganosiloxane is ahydroxyl-terminated polydimethylsiloxane.
 4. The composition of claim 3in which the ethylene-α-olefin elastomer is at least one ofethylene-propylene elastomer and an EPDM.
 5. The composition of claim 1comprising: (A) 0.5 to 30 wt % of the blend of silane-graftedethylene-α-olefin elastomer and a hydroxyl-terminatedpolyorganosiloxane; (B) Greater than 70 to 95 wt % vinyl-terminatedsilicone rubber; (C) 0.001 to 5 wt % crosslinking catalyst; and (D) 0.5to 50 wt % ethylene-α-olefin elastomer.
 6. A process for making a coldshrink article, the process comprising the steps of: (1) Forming ahomogeneous composition comprising: (A) Blend of silane-graftedethylene-α-olefin elastomer and a hydroxyl-terminatedpolyorganosiloxane; (B) 70 or more weight percent, based on the weightof the composition, of a vinyl-terminated silicone rubber; (C)Crosslinking catalyst; (D) Ethylene-α-olefin elastomer; and (E)Optionally, one or more of an additive and filler; (2) Forming thehomogeneous composition into a shaped article; (3) At least partiallycuring the shaped article; (4) Degassing the at least partially curedshaped article; (5) Stretching the cured, shaped article; and (6)Holding by mechanical means the stretched, cured, shaped article in astretched state.
 7. The process of claim 6 in which the homogeneouscomposition comprises greater than 70 to 95 wt % vinyl-terminatedsilicone rubber.
 8. A cold shrink article made from a compositioncomprising: (A) Blend of silane-grafted ethylene-α-olefin elastomer anda hydroxyl-terminated polyorganosiloxane; (B) 70 or more weight percent,based on the weight of the composition, of a vinyl-terminated siliconerubber; (C) Crosslinking catalyst; (D) Ethylene-α-olefin elastomer; and(E) Optionally, one or more of an additive and filler.
 9. The coldshrink article of claim 8 in which the composition comprises greaterthan 70 to 95 wt % vinyl-terminated silicone rubber.